1. Field of the Invention
The present invention is directed toward improved liquid ultraviolet (UV) resin compositions that comprise resin compounds blended with several defined additional chemicals. The inventive compositions have the property that when the composition is subject to ultra violet light the composition cures to a solid throughout the volume of the entire composition. This property permits the composition to be useful in applications where the possibility of exposing all of the area (and the volume beneath) of the composition to ultraviolet radiation is not present. This cure process, which continues the cure by using a trigger mechanism provided by the ultraviolet light, has been termed shadow cure. The present invention cures into areas which have no exposure to light by use of novel and surprising chemistry.
These resin compositions have enhanced properties that make them desirable materials for an ever-growing number of commercial uses. These uses include:
(a) Industrial uses such as sealing material for coils and printed circuit boards, potting compounds and sealing compounds generally and as adhesives, PA1 (b) Surgical and medical uses such as sealing of medical equipment containing electronic components, PA1 (c) A variety of automotive manufacture uses including industry potting and sealing of various automotive components, and PA1 (d) Electronic uses where tight and reliable sealing are required including encapsulation of electronic components and parts. PA1 (a) Ease of use as a one component product not requiring on-site mixing of two or more components, PA1 (b) Reduced volatile organic compounds (VOC) released into the atmosphere, PA1 (c) Rapid, deep and complete cure throughout the entire volume of the resin composition upon application of ultraviolet light and without the necessity of on-site heating. PA1 a) A liquid resin selected from the group consisting of cycloaliphatic expoxides and vinyl ethers, and mixtures thereof with epoxy polyolefins ethers; PA1 b) When component a) contains a cycloaliphatic expoxide, a hydroxy-functional material that will react with the liquid resin of element a) upon the application of an ultraviolet light stimulus; PA1 c) One or more cationic photoinitiators preferably one or more iodonomium salts that produce Lewis acid upon the application of ultraviolet light or thermal heating; PA1 d) A sensitizer material which sensitizes component c) to increase its reactivity and PA1 e) An organic peroxide that has a ten hour half life at about 65.degree. C. to 110.degree. C. PA1 a) from 25 to 95% by weight of a liquid resin selected from the group consisting of cycloaliphatic expoxides, vinyl ethers and mixtures thereof with epoxy polyolefins; PA1 b) when component (a) contains a cycloaliphatic epoxide, from 1 to 70% by weight of a hydroxy-functional material that will react with the liquid resin of component a); PA1 c) from 0.1 to 10% by weight of one or more cationic photoinitiators that produce Lewis acid upon the application of ultraviolet light; PA1 d) from 0.1 to 5.0% by weight of a sensitizer material which sensitizes component c) to increase its reactivity and PA1 e) from 0.2 to 5.0% by weight of an organic peroxide that has a ten hour half-life of about 65.degree. C. to 110.degree. C.
Advantages of the Instant Invention Include:
2. Background of the Invention
Resin compositions which cure by exposure to ultraviolet radiation are known in the art. Such compositions found in actual commercial usage today, however, in the fields discussed above are very few. An even smaller number of such compositions are known to the art which completely cure by brief exposure to ultraviolet radiation in areas not reached by such light.
3. Description of the Prior Art
Some prior art of interest is discussed below for background.
Reactions between epoxides and compounds having aliphatic hydroxyl groups have been known. Such reactions have been generally carried out at elevated temperatures by heating the reactants in the presence of basic or acid catalysts. For example, U.S. Pat. No. 2,914,490 describes the thermal reactions of a variety of epoxides with different types of polyols including copolymers containing reactive hydroxyl groups. Such reactions proceed very slowly in the presence of a catalyst at room temperature with elevated temperatures necessary to get reasonable reaction rates and useful properties.
U.S. Pat. No. 3,450,613 disclosed photopolymerizable epoxy compositions comprising the reaction product of an epoxy resin prepolymer and an ethylenically unsaturated organic acid, a photosensitizer, and optionally polyfunctional acids or bases. On exposure to ultraviolet light there is a photoinduced polymerization of the ethylenically unsaturated portion of the reaction product. The cure of the composition is completed by outside heating to bring about reaction of the epoxy resin portion of the composition. Compositions such as this, and commercial products using their type of mechanism, have very poor usefulness because of the requirement of both light and heat to effect a complete polymerization cure of the entire composition. Such compositions are often oxygen sensitive and usually have very poor thermal stability.
U.S. Pat. No. 4,256,828 describes photocopolymerizable compositions which contain epoxides, organic material with hydroxyl functionality and a photosensitive aromatic sulfonoic or iodonium salt of a halogen containing complex ion. U.S. Pat. No. 5,837,398 refers to U.S. Pat. No. 4,256,828 and describes a battery sealant composition which does not require an organic solvent.
U.S. Pat. No. 4,699,802 shows a dual curing coating method using liquid silicones curable by ultraviolet light on a substrate having no readily accessible areas to direct UV light using a process of first, irradiation, and then exposing the radiated composition to a moisture cure. See also U.S. Pat. No. 5,008,301 which shows a three mechanism curing system using separate light, heat and moisture outside mechanisms.
U.S. Pat. No. 5,017,406 describes an UV curable composition cured with polysilane with a peroxide photoinitiator. Peroxides used include dibenzoyl peroxide and hydrogen peroxide.
U.S. Pat. No. 5,712,231, in a description of the prior art, states that heat-activated peroxides may have been added to acrylic, exoxy, silicone and polyurethane systems but could not be used where heat sensitive electronic components are involved.
There has long been a need for a thermally stable, one-part, photocurable resin compositions, such as epoxy compositions, which provides a flexible or solid coating and an assured complete cure and seal. Such composition has not heretofore been provided by the many artisans working in the field.